Urban song birds are raising the pitch of their voices to make themselves heard above the background roar of the city, scientists report on Thursday.

But the sounds of city life may be harming the chaffinch, dunnock and other birds whose vocal range is unable to soar above the din.

Loud and low noise sources such as cars, planes, and machinery are placing new selection pressure on wildlife that rely on sound to attract mates and define territories.

This has been observed for the first time in great tits (Parus major), which have been found to sing higher notes near major roads and busy intersections, a ploy that could allow these urban birds to ensure that their mating calls are heard above the racket.

Birds in quieter spots such as residential neighbourhoods, on the other hand, more often dip to the bottom of their vocal register, a Dutch team reports on Thursday in Nature.

City-dwelling birds seem to be tailoring their songs to ensure maximum success with the opposite sex against a background of low-frequency urban rumblings, according to Hans Slabbekoorn and Margriet Peet of Leiden University.

The team bases its findings on recordings in and around Leiden but have now extended its work to other European cities. Slabbekoorn said: “Data from London have not been analysed yet but there is no reason to think they are different.”

Any bird species that produces songs within the frequency range of urban pollution and lack the ability to adapt their songs so they are heard may find it difficult to breed in built-up areas.